Wheels are going to be a fun thing to get for this bike. I have a set on my Six that are pretty great, Mavic Aksiums. They are a good training wheel. I picked up a set of Ksyerum's at VeloSwap, and want to put them on the Six, and then the Aksiums on the cross bike. The nice thing about that is that I already own both of them!
On the other hand, I have a couple sets of cross specific wheels from a friend. The drawback: they're tubular. A tubular tire looks like this:
The tire and the tube are one part, and are glued to a special rim with a smooth surface. The advantages are that they're a little lighter, they can run either very low or very high tire pressure and they are less likely to get a pinch flat (due to a smoother rim).
Clincher Rim Tubular Rim
Notice the clincher has a deep rim that the tire can secure into, while the tubular has a smooth rim that makes good surface for gluing to. Mounting a tubular tire is a bit of a hassle, the glue is pretty messy and it can be tough to get aligned correctly, but no less frustrating than a tight clincher! Keep an eye out for a post on mounting tubulars!